1. Field of the Invention
The present invention relates to a process for electrolytically purifying a photographic waste solution containing developer and fixing waste solutions after silver has been recovered from said waste solution, thereby degrading and removing from said waste solution those components having high COD (chemical oxygen demand) concentrations.
2. Description of the Prior Art
Black-and-white and color photography has gained wide acceptance and plates for photoprinting and X-ray photographs are being manufactured in large numbers, so large quantities of photographic waste solutions must be discharged. It is ecologically very objectionable to dump such waste solutions into the waterways without appropriate treatment, for they contain as much as tens of thousands ppm of components which are high in COD and pollute the water courses into which they are dumped. The regulations on environmental pollution are becoming stricter and are being enforced more rigorously, so the removal of such pollutants from photographic waste solutions has become a matter requiring immediate attention.
There are two conventional techniques for purifying a photographic waste solution after silver has been recovered from said waste solution: one is thermal oxidative decomposition using hypochlorite as oxidizing agent; the other is an activate sludge process. The disadvantages of the thermal oxidative decomposition process are that it requires a long heating time, involves complicated control procedures for the agents used and, lastly, the agents required are expensive. The disadvantages of the activated sludge process are that large-scale equipment, including a pool or tank for the waste solution, is required and the processing time is long. Further, neither method is successful in removing objectionable components having high COD values, so secondary treatments are necessary. These additional steps increase the operating costs. A recent method involves adding salt (sodium chloride) to waste water including organic substances and effecting electrolysis to remove those components having high COD values, but this method has not proven practical because it does not remove enough of such objectionable components. In short, none of the prior art inventions succeeds in removing almost all of the components having high concentrations of COD by electrolytic oxidation alone.